1. Field of the Invention
This invention relates to a device and method for reducing light level dynamics in an optical transmission system.
2. The Prior Art
Optical transmission systems may involve a network of many sending/receiving stations interconnected by means such as light conducting fibers and mixing elements such as star couplers. The use of star couplers is disclosed in an article by Hudson, et al, "The Star Coupler: A Unique Interconnection Component for Multimode Optical Waveguide Communications Systems," Applied Optics, Vol. 13, No. 11, November 1974, pp. 2540-2545. Another optical coupler for connecting light conducting fibers is disclosed in German Offlengungsschrift No. 29 15 114 (corresponding to U.S. Pat. No. 4,362,357).
In such optical transmission systems, the problem is often presented that the optical powers coupled into the system from the transmitters exhibit different levels at the receiver locations. Such level dynamics are caused by factors such as different coupler insertion losses and fiber attenuations on each of the links between each transmitter and each receiver. Depending upon the dynamic range, equalisation of compensation of these power fluctuations means a considerable expense in additional receiver circuitry. If left uncompensated, the level dynamics may result in an increased error rate.